Vacuum infusion device

ABSTRACT

A vacuum biased disposable infuser is provided having a liquid chamber (14) and at least one vacuum chamber (44). The liquid chamber (14) includes a liquid plunger (26) contained therein while the vacuum chamber (44) includes a vacuum plunger (48). The plungers (26, 48) are connected by an arm such that when liquid under pressure is provided to the liquid chamber (14), the vacuum plunger (48) is drawn back in the vacuum chamber (44). The device is further preloaded such that at the end of infusion, the vacuum plunger (48) does not abut against the vacuum chamber (44).

FIELD OF THE INVENTION

The present invention relates to the controlled delivery of liquids and,in particular, to portable apparatus for delivery of a medical liquidhaving a beneficial agent to a patient.

BACKGROUND OF THE INVENTION

Devices for infusing to a patient a beneficial agent such as a drugdiffused in a medical liquid are known in the art. The most commondevice utilizes an elevated glass or flexible container having abeneficial agent diffused in a medical liquid which is fed by gravity toa patient's venous system via a length of flexible plastic tubing and acatheter. The rate of flow in this type of device is commonly regulatedby an adjustable clamp on the tubing. This set-up suffers from thedrawback of requiring a relatively stationary patient and is dependenton the height differential between the medical liquid and the patientfor accurate delivery rates.

An additional type of infusion device utilizes electro-mechanicalcomponents and a pump to provide fluid propulsion of the medical liquidfor infusion into the patient. Such electronically controlled infusiondevices, however, suffer from several drawbacks, including the cost ofsuch electrical components as well as the limit such electricalcomponents and the necessary power source place on the size and thusportability of the device.

Devices in the art are also utilized which employ an elastomeric bladderwhich contains the medical liquid to be infused under pressure forinfusion. A typical elastomeric bladder device includes housing, a plugfixed in one end of the housing which includes aperture that extendsthrough the plug, and a tubular elastomeric bladder in the housing forreceiving the liquid under pressure. One end of the bladder is sealinglyattached to the plug, with the interior of the bladder communicatingwith the aperture of the plug. A conduit connected to the plug aperturedefines with the aperture a dispensing passageway for transporting themedical liquid from the bladder to the infusion site of the patient. Aflow regulator is disposed somewhere in the dispensing passageway forpermitting the medical liquid to flow from the bladder to the dispensingpassageway at a predetermined rate into the patient.

Another type of device utilizes a syringe-type construction having aplunger disposed within and making sliding, sealing contact with theinterior surface of the syringe barrel. A biasing means such as a springor an elastomeric band is also provided between the plunger and thehousing. Medical liquid to be infused is received under pressure withinthe interior of the barrel in a chamber defined by the interior of thebarrel and the plunger. The pressurized medical liquid forces theplunger to bias the biasing member thereby providing a source of medicalliquid under pressure. The pressurized medical liquid is provided to apatient through the conduit means similar to the elastomeric bladdertype device.

A particular problem in the infusion devices in the art is achieving arelatively constant flow rate for the infusion of the liquid. Therelatively constant flow rate is particularly important when infusionover extended periods of time, such as 24 or 48 hours, is required forthe drug therapy. In the infusion devices utilizing elastomericbladders, such relatively constant flow rates have been achieved bymeans such as prestressing the elastomeric bladder and the use of costlybladder material. The use of such additional prestress housing andexpensive bladder material, of course, adds to the costs of suchdisposable infusers. In the syringe-type infusion devices, the rate ofinfusion is restricted to a relatively short period of time because ofthe accuracy problem found in such designs.

What would thus be desirable would be a disposable infuser device whichis able to give relatively constant flow rates over extended periods ofinfusing while maintaining a comparatively low manufacturing andmaterials cost factor. The present invention achieves theserequirements.

SUMMARY OF THE INVENTION

The present invention provides a syringe-type disposable infusion devicehaving as a biasing source a vacuum. The present device includes aliquid chamber which in a preferred embodiment is a cylindrical barrel.At one end of the cylindrical barrel, a plug is fixed in housing whichincludes an aperture that extends through the plug. A conduit isconnected to the exterior plug aperture to define a dispensingpassageway for transporting the liquid from the liquid chamber to theinfusion site of the patient. A flow regulator is disposed somewhere inthe dispensing passageway for permitting the liquid to flow from theliquid chamber to the dispensing passageway and at a predetermined rateinto the patient.

At the opposite end of the cylindrical barrel, a liquid plunger isprovided in sliding sealing engagement with the interior surface of theliquid chamber. Extending posteriorly from the liquid plunger is an arm.

Additionally provided is at least one source of vacuum or a vacuumchamber. In the preferred embodiment, the vacuum chamber is acylindrical barrel which is sealed at one end. At the opposite end, avacuum plunger is provided in sliding sealing engagement with theinterior surface of the vacuum chamber. An arm is provided to establisha direct link between the vacuum plunger in the vacuum chamber and theliquid plunger in the liquid chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an infusion device made in accordancewith the principles of the present invention;

FIG. 2 is a graph of the pressure exerted on the vacuum plunger of thedevice of FIG. 1 as a function of the position of the vacuum plunger;

FIG. 3 is an overhead view of the device of FIG. 1 in the loadedposition;

FIG. 4 is an overhead view of the device of FIG. 1 in the unloadedposition;

FIG. 5 is an overhead view of the device of FIG. 1 in the storageposition;

FIG. 6 is a cross-sectional view of a preferred embodiment of a two-wayvalve made in accordance with the principles of the present invention;

FIG. 7 is a cross-sectional view of connector housing of the device ofFIG. 6; and

FIG. 8 is a cross-sectional view of attachment housing of the device ofFIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a perspective view is seen wherein a devicemade in accordance with the principles of the present invention isdesignated generally by the reference number 10. The device 10 includesa first tubular housing defining a rigid cylindrical barrel 12. Therigid cylindrical barrel 12 defines a tubular liquid chamber 14 whichincludes an interior 16. The rigid cylindrical barrel 12 is preferablymolded of a transparent material such as plastic to enable clear visualinspection of the interior 16 of the liquid chamber 14. Imprinted,inscribed or otherwise applied to the barrel wall, a graduated volumescale 18 is also preferably provided.

Sealingly attached to the anterior end of the liquid chamber 14 is aplug housing 20. The plug housing 20 defines an access apertureextending therethrough which establishes fluid communication with theliquid chamber interior 16. Also sealingly attached to the plug housing20 is a fluid conduit which includes tubing 22. The tubing 22 includes aproximal end and a distal end. Secured on the distal end of the tubing22 in fluid communication with the interior of the tubing 22 is a flowrestrictor 24. In a preferred embodiment, the flow restrictor 24 is aglass capillary tube. The flow restrictor 24 can be contained in housingwhich can preferably include a luer connector 25 for connection to acatheter (not shown) having a cooperative luer connector.

The tubing 22 proximal end is secured to the plug with the interior ofthe tubing 22 in fluid communication with the access aperture. While thetubing 22 can be permanently secured to the plug housing 20 by adhesiveor the like, in a preferred embodiment the tubing 22 can bedisconnectable from the plug housing 20. A preferred embodiment of suchdetachable connector will be described in detail below.

A liquid plunger 26 is contained within the liquid chamber 14. Theliquid plunger 26 includes a pair of outwardly projecting ribs 28 whichare sized and shaped to establish a sliding, sealing engagement with theinterior surface 16 of the barrel 12. The outwardly projecting ribs 28of the liquid plunger 26 are preferably formed integrally with theliquid plunger 26 and can preferably be made of a polypropylene coatedrubber, silicon rubber, coated neoprene, or a similar type of materialto provide a sealing, sliding engagement while minimizing the frictionbetween the liquid plunger 26 and the interior surface 16 of the barrel12. Additionally, the anterior surface 30 of the liquid plunger 26exposed to the interior 16 of the liquid chamber 14 is preferably formedin a conical shape which cooperates with the conically shaped housing 32at the anterior end of the liquid chamber 14 to form a sealingengagement when the liquid chamber 14 is empty. This insures thatsubstantially all of the liquid in the liquid chamber 14 is expressedout of the liquid chamber 14 during infusion.

Provided extending from the posterior side of the liquid plunger 26 is aplunger arm 36. Provided at the posterior periphery of the plunger arm36 is an enlarged diameter protrusion which defines a plunger head 38.

Additionally provided and secured to the tubular liquid chamber 14 byconnector means 40 is at least one additional tubular housing againhaving a rigid cylindrical barrel 42. This second rigid cylindricalbarrel 42 defines a tubular vacuum chamber 44 having an interior surface50. Again, the second rigid cylindrical barrel is preferably molded of atransparent material such as plastic to enable clear visual inspectionof the interior of the vacuum chamber 44. While in the preferredembodiment depicted herein, two vacuum chambers 44 are provided, thepresent invention contemplates any number of vacuum chambers, from oneto more than two, which can then be utilized in combination to providedifferent forces on the liquid as explained in detail below.

The anterior end of the vacuum chamber 44 includes housing 46 whichseals the vacuum chamber 44. This anterior housing 46 is preferably flatto reduce the surface area exposed to the interior of the vacuum chamber44 to the smallest possible amount. Additionally provided in the vacuumchamber 44 is a vacuum plunger 48. The vacuum plunger 48 includes a pairof outwardly projecting ribs 52 which are sized and shaped to establisha sliding, sealing engagement with the interior surface 50 of the vacuumchamber 44. Again, the outwardly projecting ribs 52 of the vacuumplunger 48 can be preferably made of a polypropylene coated rubber,silicon rubber, coated neoprene or a similar type of material to providea sliding, sealing engagement while minimizing the friction between theplunger 48 and the interior surface 50 of the vacuum chamber 44. Unlikethe liquid plunger 26, the vacuum plunger 48 includes at its anteriorend facing the interior of the vacuum chamber 44 a flat surface 56 toreduce the surface area of the vacuum plunger 48 exposed to the vacuumwithin the vacuum chamber 44. Provided extending from the posterior sideof the vacuum plunger 48 is a plunger arm 58. Provided at the posteriorperiphery of the plunger arm 58 is a plunger head 60.

Because of the characteristics of the vacuum which provides the bias toprovide a pressurized source of liquid, an essentially constant force isapplied on the vacuum plunger 48 throughout the length of the vacuumchamber 44. This constant force results from the atmospheric pressurewhich provides a force on the posterior of the vacuum plunger 48 whichis a constant force depending on the atmospheric pressure to which thedevice is exposed. Because a vacuum is contained on the anterior of thevacuum plunger 48, a nearly constant force of approximately zero isapplied to the anterior of the vacuum plunger 48 throughout the lengthof the vacuum chamber 44. It is thus seen that throughout the length ofthe vacuum chamber 44 approximately constant forces are applied bothanteriorly and posteriorly to the vacuum plunger 48.

However, because nature does not know a perfect vacuum, a small amountof force is applied on the anterior end of the vacuum plunger 48.Throughout most of the length of the vacuum chamber 44, this smallamount of force is sufficiently "diluted" by the larger "amount" ofvacuum to result in a negligible force on the vacuum plunger 48. As thevacuum plunger 48 approaches the closed end 46 of the vacuum chamber 44,the percentage of the evacuated area which is a "perfect" vacuumdeclines while the area of the evacuated area which is a "force"increases. This results in a logarithmic pressure spike applied to theanterior of the vacuum plunger 44 near the closed end 46 of the vacuumchamber 44. This pressure spike works to offset the atmospheric pressureon the posterior side of the vacuum plunger 48 which results in a dropin the biasing force on the vacuum plunger 48.

Referring to FIG. 2, the forces applied on the anterior end of thevacuum plunger 48 are seen as a function of the distance along thevacuum chamber 44 that the vacuum plunger 48 travels. It is seen thatthroughout most of this distance a relatively constant, extremely smallforce (a) is applied which results in a near constant infusion of theliquid. It is further seen that near the area where the vacuum plunger48 approaches the closed end 46 of the vacuum chamber 44, the forceapplied on the anterior of the vacuum plunger 48 spikes upwardly (b) andapproaches atmospheric pressure.

While this phenomena has been recognized in the art, attempts toeliminate this phenomena have not been satisfactory which has resultedin a lack of commercialized infusers utilizing a vacuum source as abiasing means. The attempts in the prior art to reckon with thisphenomena are primarily attempts to perfect the vacuum contained in theevacuated area in an attempt to minimize this pressure spike. Whilethese attempts to perfect a vacuum are theoretically possible, inpractice such perfection of the vacuum source quickly results inmanufacturing techniques such as manufacturing in a vacuum which arecost prohibitive to a disposable infuser. The present device 10 employsmeans for preloading the vacuum which prevents this force from resultingin inaccurate infusion.

The vacuum plunger 48 is connected to the liquid plunger 26 by means ofa removable support 62 which extends between the vacuum plunger arm 58and the liquid plunger arm 36. Thus, between the vacuum plunger 48 andthe liquid plunger 26, a generally U-shaped arm extends to transfer theforce exerted on the vacuum plunger 48 to the liquid plunger 26 tocreate in the liquid chamber 14 a source of pressurized liquid. While inthe presently depicted embodiment, this connection is generallyU-shaped, the present invention, of course, contemplates the use offunctionally equivalent shaped arm and plunger orientations which resultin a functional equivalent to the present device.

Referring now to FIGS. 3, 4 and 5, overhead views of the device of FIG.1 are seen. As is seen particularly in FIGS. 3 and 4, the liquid plunger26 is offset posteriorly from the vacuum plunger 48 a distance (d). Asis seen particularly in FIG. 4, this offset distance (d) results in theliquid plunger 26 abutting against the anterior housing 20 of the liquidchamber 14 before the vacuum plunger 48 abuts against the closed end 46of the vacuum chamber 44. This distance (d) is referred to herein as thepreload distance. Referring to FIG. 2, this preload distance (d) iscalculated to allow infusion to be completed before the vacuum plunger48 approaches the pressure spike applied on the anterior portion of thevacuum plunger 48. Thus, by utilizing this preload distance (d), therate of infusion is seen to be relatively constant throughout the entireinfusion.

Referring now to FIG. 5, the application of this preload distance (d) onthe device is described. The device is seen in storage in which thevacuum plunger 48 as well as the liquid plunger 26 is abutted againstthe anterior of the respective chambers 14, 44. Thus, when in storage inthis position, no vacuum or bias is applied to the vacuum plunger 48 andthus the achieved purity of the vacuum is assured during storage andshipping.

Prior to use of the device 10, the removable support 62 is attached tocomplete the generally U-shaped arm between the vacuum plunger 48 andthe liquid plunger 26. The removable support 62 includes at least oneslot 66 (best seen in FIG. 1), the specific number of which correspondto the specific number of vacuum chambers 44, and defines a posterior 67and anterior surface 69. Prior to use, the removable support 62 is slidover the vacuum plunger arm 58. The size of the slot 66 is sufficientlylarge to slide over the vacuum plunger arm 58 but is smaller than thediameter of the plunger head 60. Thus, the vacuum plunger head 60 abutsagainst the posterior surface 67 of the removable support 62.

The removable support 62 is oriented such that the plunger head 38 ofthe liquid plunger arm 36 abuts against the anterior surface 69 of theremovable support 62. Thus, when the removable support 62 is attached tothe device 10, the distance between the vacuum plunger arm 67 and theliquid plunger arm 36 is established as the thickness of the removablesupport 62. The removable support 62 in conjunction with the plungerarms 36, 58 and plunger heads 38, 60 act as means for applying to anunloaded device a preload to the vacuum source. To then load theinfuser, a liquid containing a beneficial agent dispersed therein isadded under pressure to the liquid chamber 14, the force of which drawsthe vacuum plunger 48 posteriorly and results in a source of pressurizedliquid in the liquid chamber 14.

Because nature does not know a perfect vacuum, the vacuum plunger 26will never freely abut against the closed end 46 of the vacuum chamber44. The small distance at which the vacuum plunger 26 comes to rest fromthe closed end 46 of the vacuum chamber 44 is referred to as a tolerancedistance (t). This tolerance distance (t) depends on the purity of thevacuum achieved.

The amount of preload distance (d) needed to assure desired accuracy ofinfusion can be determined as a function of the tolerance distance (t).Initially, we know at any given distance of the vacuum plunger 48 alongthe vacuum chamber 44, the forces exerted on the anterior and posteriorsurface of the vacuum plunger 48 must be equal. Since f=PV, where P ispressure, V is volume, and f is force, it is known:

    P.sub.1 V.sub.1 =P.sub.2 V.sub.2                           (1)

where P₁ is the pressure exerted on the posterior surface of the vacuumplunger 48, P₂ is the pressure exerted on the anterior surface of thevacuum plunger 48. V₁ is the volume of the vacuum chamber 44 posteriorto the vacuum plunger 48, and V₂ is the volume of the evacuated portionof the vacuum chamber 44.

It is also known that V=(πD² /4)(h) for a cylinder where D is thediameter and h is the height of the cylinder. Further, the height of thevacuum chamber 44 as a whole is x+t where x is the length the vacuumplunger travels. Substituting into equation (1), ##EQU1##

Further, we can assume that P₁ is at atmospheric pressure or 14.6960psig. Utilizing various values for x and t, we obtain the followingvalues of P₂ in psig:

                  TABLE 1                                                         ______________________________________                                        VERIFICATION OF PRESSURE CHANGE                                               WITH PISTON TRAVEL                                                            FORMULA IS P.sub.2 = P.sub.1 (t)/(t + x)                                      DISTANCE   DISTANCE t in inches                                               x in inches                                                                              0.001    0.002  0.005  0.01 0.02                                   ______________________________________                                        3.0        0.005    0.010  0.024  0.049                                                                              0.097                                  2.0        0.007    0.015  0.037  0.073                                                                              0.146                                  1.5        0.010    0.020  0.049  0.097                                                                              0.193                                  1.0        0.015    0.029  0.073  0.146                                                                              0.288                                  0.5        0.029    0.059  0.146  0.288                                                                              0.565                                  0.2        0.073    0.146  0.358  0.700                                                                              1.336                                  0.1        0.146    0.288  0.700  1.336                                                                              2.449                                  ______________________________________                                    

Thus, when the vacuum plunger 48 is at various distances (x) along thelength of the vacuum chamber 44, the evacuated portion exhibits thefollowing degree of vacuum:

                  TABLE 2                                                         ______________________________________                                        DEGREE OF VACUUM*                                                             DISTANCE DISTANCE t in inches                                                 x in inches                                                                            0.001    0.002    0.005  0.01   0.02                                 ______________________________________                                        3.0      99.97%   99.93%   99.83% 99.67% 99.34%                               2.0      99.95%   99.90%   99.75% 99.50% 99.01%                               1.5      99.93%   99.87%   99.67% 99.34% 98.68%                               1.0      99.90%   99.80%   99.50% 99.01% 98.04%                               0.5      99.80%   99.60%   99.01% 98.04% 96.15%                               0.2      99.50%   99.01%   97.56% 95.24% 90.91%                               0.1      99.01%   98.04%   95.24% 90.91% 83.33%                               ______________________________________                                         *100% represents absolute vacuum                                         

By utilizing these values, the desired degree of accuracy can beachieved by knowing the tolerance of manufacture as well as the lengthof the vacuum chamber 44. For example, if a tolerance of between 0.001to 0.002 inches is achieved and an accuracy of ±5% is desired,approximating from TABLE 2, a preload distance of greater than 0.5inches is required.

Additionally, as is seen the force executed as the vacuum plunger 48 isdependent on the atmospheric pressure executed on the device 10. Tounderstand how differences in the atmospheric pressure could affect thepresent device 10, atmospheric conditions were obtained from TheNational Weather Service for the following sample cities:

                  TABLE 3                                                         ______________________________________                                        ATMOSPHERIC CONDITIONS                                                                Boston Los Angeles                                                                              Chicago   Denver                                    ______________________________________                                        ELEV*     15 ft.   270 ft.    658 ft. 5,283 ft.                               PRESSURE**                                                                    MAX       1.036    1.019      1.032   .843                                    MIN        .948     .975       .956   .792                                    AVG       1.001     .997       .980   .823                                    RANGE***  ±4.4% ±2.2%   ±3.8%                                                                              ±3.1%                                MID                                                                           ______________________________________                                         *Above sea level                                                              **In Atmos                                                                    ***In percentages                                                        

It is thus seen that the changes in atmospheric pressure in a givensample city results in a maximum change in biasing pressure of ±4.4%,which is well within a satisfactory tolerance range of infusion.Additionally, differences in average atmospheric pressure for differentgeographic areas can simply be compensated by adjusting theconcentration of beneficial agent in the medical liquid by a pharmacist.

Referring now to FIGS. 6 through 8, the preferred embodiment of valvemeans 70 contained in the plug housing 20 of the liquid chamber 14 isseen. Referring first to FIG. 7, a plug portion 68 of the valve means 70in the loading or storage mode is seen. The valve includes a connectorhousing 72 which defines a connector 74. The connector can preferably bea female luer. The female luer includes an aperture 76 defined thereinwhich is in fluid communication with a duck-bill valve 80. The duck-billvalve 80 includes a pair of lips 82. Contained on the downstream side ofthe duck-bill valve 80 is an access aperture 83 which is in liquidcommunication with the interior of the liquid chamber 14. Thus, to loadthe liquid chamber 14, a device such as a syringe capable of providingliquid under pressure and having a cooperating connector such as a maleluer is attached to the female luer and the liquid contained within thesyringe is expressed under pressure past the duck-bill valve 80 to theinterior of the liquid chamber 14 to define a source of pressurizedliquid. After loading, the duck-bill valve 80 contains the liquid underpressure within the liquid chamber 14.

Referring now to FIG. 8, an outlet conduit 84 of the valve means 70 isseen in detail. The tubing 22 is secured to a filter housing 86contained on the outlet conduit 84 by means such as an adhesive. Thefilter housing 86 defines a filter aperture which contains a filter 88in fluid communication with the interior of the tubing 22. The filter 88is utilized to prevent non-dissolved beneficial agent contained in themedical liquid from entering the fluid conduit and thus the venoussystem of the patient. The filter 88 can be preferably made of stainlesssteel, platinum wire, or other suitable material or of any of a varietyof polymers such as polytetrafluoroethylene, having a porous ormultifilament configuration capable of operating as a screen and whichwill be substantially unreactive in the presence of the beneficialagent.

The outlet conduit 84 further includes housing 92 which defines aconnector 94 which acts cooperatively with the connector 74 on the plugportion 68. In the preferred embodiment, this cooperating connector 94is a male luer. The housing further defines an aperture 96 in fluidcommunication with the filter 88. Extending from the aperture 96 is ablunt cannula 98 defining an internal channel in fluid communicationwith the aperture 96.

The blunt cannula 98 extends a distance from the housing 92 which isdefined by the duck-bill valve 80. Specifically, The blunt cannula 98must extend sufficiently from the housing 92 to open the duck-bill valve80 when the connectors 74, 94 are secured. While extending the bluntcannula 98 past the duck-bill valve 80 does satisfactorily open theduck-bill valve 80, it has been found that such extension results in anamount of leakage of the liquid stored in the liquid chamber 14proportional to the distance past the duck-bill valve 80 that the bluntcannula 98 extends.

Thus, in a preferred embodiment, the blunt cannula 98 extends into theduck-bill valve 80 sufficiently to separate the lips 82 of the duck-billvalve 80 without penetrating through. In a further preferred embodiment,the outer periphery of the diluent cannula 98 is about flush with theend of the duck-bill valve 80. In this embodiment, small manufacturingtolerances will not appreciably affect the performance of the valve assufficient penetration is assured to separate the lips 82 but extensiveleakage is prevented.

After loading, to use the device 10, the male luer is connected to thefemale luer. This forces the blunt cannula 98 into engagement with theduck-bill valve 80. When the male luer and female luer are secured, theopen end of the blunt cannula 98 extends into the duck-bill valve 80 toestablish fluid communication with the interior of the liquid chamber 14(best seen in FIG. 6). Thus, the liquid under pressure in the liquidchamber 14 rushes into the blunt cannula 98, past the filter 88, intothe tubing 22, and past the flow restrictor 24 contained in the tubing22 to the patient.

It should be understood that various changes and modifications to thepreferred embodiments described herein will be apparent to those skilledin the art. Such changes and modifications can be made without departingfrom the spirit and scope of the present invention and withoutdiminishing its attendant advantages. It is, therefore, intended thatsuch changes and modifications be covered by the appended claims.

What is claimed is:
 1. A device for infusing liquid comprising:a liquidchamber adapted to receive a liquid under pressure, the liquid chamberhaving a liquid plunger contained within the liquid chamber and a fluidconduit extending from the liquid chamber; a vacuum chamber, the vacuumchamber having a vacuum plunger contained within the vacuum chamber; anarm connecting the liquid plunger and the vacuum plunger such that whenliquid is introduced into the liquid chamber under pressure the vacuumplunger biases; and means for preloading the vacuum plunger such thatthe vacuum plunger does not abut an end of the vacuum chamber housingafter infusion.
 2. The device of claim 1 further wherein the preloadmeans can be disabled such that the device can be stored without apreload.
 3. The device of claim 1 wherein the liquid chamber is tubular.4. The device of claim 1 wherein the vacuum chamber is tubular.
 5. Thedevice of claim 1 wherein the liquid plunger further includes a plungerarm, the vacuum plunger further includes a plunger arm, and a removablesupport connects the plunger arms thus forming a generally U-shaped arm.6. The device of claim 5 wherein the removable support offsets theliquid plunger from the vacuum plunger the preload distance therebyacting as the preload means.
 7. An infusion device comprising:a tubularhousing for receiving a liquid having at one end an outlet aperture; aliquid plunger slidably mounted in the liquid tubular housing; at leastone tubular housing having a closed end defining a vacuum chamber; avacuum plunger slidably mounted in the closed end tubular housing; anarm connecting the liquid plunger and the vacuum plunger such that whenliquid is introduced under pressure in the liquid tubular housing viathe outlet aperture the vacuum plunger biases; and means for preloadingthe vacuum plunger such that upon expulsion of the liquid from theliquid tubular housing the vacuum plunger is a preload distance from theclosed end of the vacuum housing.
 8. The device of claim 7 furtherwherein the preload means can be disabled such that the device can bestored without a preload.
 9. The device of claim 7 wherein the liquidplunger further includes a plunger arm, the vacuum plunger furtherincludes a plunger arm, and a removable support connects the plungerarms thus forming a generally U-shaped arm.
 10. The device of claim 9wherein the removable support offsets the liquid plunger from the vacuumplunger the preload distance thereby acting as the preload means.